This invention relates to variable capacity vane compressors which are suitable for use as refrigerant compressors of air conditioners for automotive vehicles.
There are known variable capacity vane compressors which are capable of controlling the capacity of the compressor by varying the suction quanitity of a gas to be compressed. As one of such vane compressors a variable vane compressor is known e.g. by Japanese Provisional Patent Publication (Kokai) No. 62-129593, which is provided with a cam ring c having an inner peripheral surface with an elliptical cross section which forms a chamber b accommodating therein a rotor a with a circular cross section, as shown in FIG. 1, and an angularly movable control plate f having its outer peripheral edge formed with diametrically opposite arcuate cut-out portions e, e communicating inlet ports d, d to compression chambers h, h, respectively, as shown in FIG. 1. The control plate f is disposed to move in circumferential opposite directions in response to a difference between pressure on a lower pressure side and pressure on a higher pressure side, to vary the circumferential positions of the cut-out portions e, e, thereby controlling the capacity or delivery quantity of the compressor. During the operation of the above compressor, a refrigerant gas to be compressed is sucked from each inlet port d into a space defined between adjacent vanes g, g, as the volume of a compression chamber h is increased during a suction stroke thereof, in accordance with the rotation of the rotor a in a counter-clockwise direction as viewed in FIG. 1, and then the sucked gas is compressed, as the volume of the compression chamber h is reduced during a compression stroke thereof. Then the compressed gas is discharged from an outlet port j. When the control plate f is displaced to an extreme circumferential position in which the maximum capacity of the compressor is obtained, i.e. in the clockwise direction as viewed in FIG. 1, opposite ends e1, e2 of each cut-out portion e are aligned with respective opposite ends d1, d2 of the corresponding inlet port d, whereby the compression of the refrigerant gas is commenced at a point A shown in FIG. 1 to achieve maximum or full capacity operation. On the other hand, when the control plate f is displaced to an opposite extreme circumferential position in which the minimum capacity of the compressor is obtained, i.e. in the counter-clockwise direction as viewed in FIG. 1, the opposite ends e1, e2 of each cut-out portion e are positioned on a downstream side of the downstream end d1 of the inlet port d, with respect to the rotational direction of the rotor a, whereby the compression of the refrigerant gas is commenced at a point B shown in FIG. 2 to achieve minimum capacity operation.
During the minimum capacity operation, the upstream end e2 is positioned on a downstream side of the downstream end d1 of the inlet port d, apart therefrom by a distance L. As a result, compression of the gas is effected at the portion L during high speed rotation of the compressor. More specifically, the gas cannot laterally escape while it travels along the distance L, and when having passed the distance L, it is prevented from leaking into a lower pressure side through the cut-out portion e by the inertia force of the gas flow due to rotational high speed of the compressor. The compression of the gas over the distance L is unnecessary or superfluous and undesirable because it causes resistance of the compressed gas against the rotation of the vane g of the rotor a. If the cut-out portion e is prolonged so that its upstream end e2 becomes closer to the downstream end d1 of the inlet port d, in order to avoid the above unnecessary compression, the compression chamber h on the suction stroke is disadvantageously communicated with the compression chamber h on the discharge stroke, which is located on an upstream side of the compression chamber on the suction stroke, through the prolonged cut-out portion e during the full capacity operation of the compressor.